1. Field of the Invention
The present invention relates to a laser processing apparatus and a laser processing method, in which liquid is applied to a surface of a substrate such as a semiconductor wafer or a glass substrate for use in liquid crystal displays, and the substrate covered with liquid is scanned with a laser beam and thereby processed.
2. Description of the Related Art
Methods of manufacturing semiconductor devices include steps of processing the surface of a substrate, by using a laser beam. Among these steps are: processing a thin film such as an insulating film, a metal film or a resist film; cutting dicing lines; removing resist films from alignment marks before exposing the substrate to light (i.e., step of exposing the alignment marks).
For example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-224878, there is described a technique of forming a dicing line by scanning a laser beam on a substrate surface. In addition, in Jpn. Pat. Appln. KOKAI Publication No. 2003-249427, there is described a technique of, before carrying out exposure to a substrate, removing a resist film on the mark by means of a laser beam in order to expose the alignment mark formed in advance on the substrate. The laser beam has a large amount of energy, and enables alignment with high precision, and thus, is suitable for such a processing.
In a laser processing apparatus described in the foregoing Jpn. Pat. Appln. KOKAI Publication No. 2002-224878, as shown in FIG. 1, a rotatable chuck 13 is provided in a cap 11 by means of a drive mechanism 12. This chuck 13 is moved and aligned in an X direction and a Y direction by means of a moving mechanism. In this manner, a laser beam 18 is irradiated from a laser image forming optical system unit 14 (hereinafter, referred to as a “optical system unit”) to a resist film on an alignment mark of a substrate 10 held on the chuck 13 to remove the resist film. At this time, a transparent plate 15 consisting of quartz glass is disposed in an opposite manner to be slightly spaced from the substrate 10. Then, while pure water is supplied from one opening to a gap between the substrate 10 and the plate 15, the pure water is suctioned by the other opening. In this manner, a chip produced during a laser dicing processing operation is prevented from adhering to a surface of the substrate. After laser dicing processing, the plate 15 is raised, and the substrate 10 is rotated at a high speed. Then, water is cut from the top of the substrate 10, and the substrate 10 is dried.
In the meantime, in the laser dicing processing operation, there is a request for aligning the optical system unit 14 and the substrate 10 with each other with very high precision. However, in a conventional apparatus shown in FIG. 1, while pure water is supplied from one side between the transparent plate 15 and a surface of the substrate 10, the laser dicing processing operation is carried out by suctioning the pure water on the other side. Thus, at a time point at which the processing operation has terminated, the water adheres to a bottom face of the plate 15.
On the other hand, in the laser processing apparatus, in order to improve throughput, after the laser processing operation has been carried out with respect to one substrate, a next substrate is transported into the apparatus immediately, and a processing operation is carried out with respect to the next substrate. That is, immediately after the preceding substrate processing operation has terminated, the succeeding substrate alignment is carried out. Thus, there is no time for the bottom face of the plate 15 to dry. Thus, in a state in which water droplets have adhered to the bottom face of the plate 15 or in a state in which a moisture component has adhered to the bottom face of the plate 15 (in a state in which the plate becomes cloudy in a non-transparent manner), the succeeding substrate alignment is carried out. In such a state, a notch on the substrate side or an orientation flat (alignment site) is hardly seen upwardly, thus making it difficult to clearly identify and detect the alignment site. As a result, the optical system unit 14 and the substrate 10 cannot be aligned with very high precision, and a processing reliability is degraded.